Shaders work well for this type of compositing.  I don't think there is any need to store the alpha value in the video file.

On Fri, Aug 1, 2008 at 7:25 PM, Spencer Russell <spencer.f.russell@gmail.com> wrote:
I'm mixing video by background subtracting it and then setting the
background transparent (alpha = 0), then texturing each video onto
overlapping rectangles to achieve a compositing effect.

I need to record the different videos with [pix_record] and then play
them back later while preserving the alpha somehow, so I was thinking
that I could just replace all the transparent part with bright pink or
something and store it as regular photo jpeg frames, and then later
set all the bright pink parts to transparent when I read the video
back.

I'm having trouble with both sides of the conversion, though. Perhaps
there's a better approach entirely?

thanks,
spencer

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